Pesticide Drift and Its Effect on Cholinesterase Levels of Birds in Non-Target Areas of the Buena Vista Marsh

Pesticide drift from the aerial spraying of agricultural chemicals and its effects on the cholinesterase levels of birds in non-target areas of the Buena Vista Marsh, Wisconsin, was investigated. Surface water samples were also surveyed for pesticide residues. Brain cholinesterase activity was determined in birds from wildlife management lands adjacent to agricultural areas. Pesticide drift was sampled by the use of nylon collection screens and analyzed by gas chromatography for some of the commonly used cholinesterase inhibiting pesticides. Residues of pesticides were found in 71% of the air samples collected on 2 study areas. Parathion and diazinon were found in the highest concentrations (up to 200 micrograms of pesticide/m^2 screen) with malathion, monocrotophos, dimethoate, disulfoton, fenthion, and phorate being present in lesser amounts. A decline in the brain cholinesterase levels of red­ winged blackbird (Agelaius phoeniceus) and savannah sparrow (Passerculus sandwichensis) was found throughout the spraying season, indicating possible exposure of the birds to cholinesterase inhibiting pesticides. Low cholinesterase levels were also found early in the season which may have resulted from the birds consuming treated seeds during the planting season. Results indicate that pesticides are drifting over non­ target areas of the Buena Vista Marsh and possibly in amounts high enough to produce a measureable effect on native birdlife. Preliminary study indicates that pesticides may also be moving through the ecosystem via surface water drainage